Production of pure carbon dioxide



Jan- 12, 1954 w. K. Ll-:wls ET AL PRODUCTION OF PURE CARBON DIOXIDE 2 Sheets-Sheet l Filed May 12. 1949 bs M otzborrlag |II s i TEE m lv N3 mw. Q m. V 0m, Iv 9 fim, mim m law* N Gm, 0zrr um AI 5 .H .T bm sd m* m .L n mmz .v u f E, .mm um NN zu z. I J v. E m ll nmmw 4 .fzmum Ow Wa w MlwlnwlMw/IMIIMU w \\W./U MWM .mgn 8 i, .5.2. fica. Izimwwz |N: FI/Id//Idk 4/ II/ mw wuw z w. DN Ow Jan. 12, 1954 w, K, LEWIS ET AL 2565,97]

PRODUCTION OF 'PURE CARBON DIOXIDE Filed May 1'2, 1949 2 sheets-sheet 2 CO 4 '2 7 4 coa 5 iJOmDE iHow-CIDE 1 12 TCCHCO,a 5 Q HOT '7 L C O xlDE -JZ 4- L CO,z T

x V x Oxuae E1=L 1'2 T T io L V J? Li V 12 GTS aAToE o T a E E I GAS T COZ 9 'ZgC-ENERATQQ 6 L CO COfz Fte-5 Fra-'Z 'CJ'r-ren K. Lewis a b Edwin 2.61111; Land Venf`5 bg Obbor'ne Patented Jan. 12, 1954 UNITED sT'rEs :PATENT OFFICE 2565971 PRODUCTION or PURE `cARBoN DroxmE. Warren K. Lewis, Newton, ana Edwin R. Ginilana,

Arlington, Mass.,f assignors to Standard Oil Development'flompany, a corporation of Dela- Wal'e .Application May: 12, 1949,V Serial No.. 92,812

This invention. relates to the production of pure carbon clioxideffrom oxidizable carbonaceous material; and particularly to the production of' carbon dioxide free of inert gases, suchfas nitrogen. More particularly, the invention is concerned with the oxidation of' carbonaceous material by means-of 'solid oxidizing agents, such as metallic oxides as the source of oxygen.

At present there. are two industrial sources of carbon dioxide,. namely, as by-product from alcohol fermentation and as recovery from flue gases. The carbon dioxide produced in the former process is pure andV cheap but limited in amount. The latter sourcerequiresA absorption of the COz in carbonato solutions followed by boiling to release the .pure gas. Thisoperation is perfectly workablebut cumbersome and consumes very large quantities of heat. The amount of heat required for, recovery7 of COz from fiue gas is so large that it` is not uncommon to burnv extra fuel over. and above. thatnecessary to make the COz. Ihighly desirable..

In the production of flue gas, the oxidizing agent generally employed is air. The use'of air introduces into the product gas large amounts.

of incrt gases, suchasnitrogen, which complicate the concentration of'COz by condensation or absorption.

It is, thereforeLthe .principal object of this invention to provide4 an. improved process for producing pure carbon dioxide with the aid of solid oxidizing materials possessing the necessary oxidation potential as the Oxygen` transfer agent under controlled reaction conditions.

Itis a further object of .this invention to provide a process for the conversion ofl oxidizable carbonaceous material; particularly, finely-'divided coal and coke tocarbon dioxide.

A more specific object" of this invention is to provide a process of the type` specified which willv p'ermit oxidation ofiithe carbonaceous material bymetallicV oxides; without contaminatingV the carbon dioxide with inerti'gases, such as nitrogen.

It is also an object of' this' invention to produce carbon dioxideunder" pressure; thus yobviating the necessity of compressin'g' the'carbon dioxide.

These and other'objects` of the invention will be 'apparentfrom thedescription 'to follow.

The source of'carbon from' which the carbon dioxide-is prepared'maybe. any oxidizable carbonaceousmaterial; suchas charcoal, coal, coke, heavy distillate oil; residual oils. gaseous hydro- A cheapv source of COz is, therefore,V

6` laims. (Cl. 23-150) carbons, peat, shale, oil sands, lignite, bitumenr,

etc. Charcoal and coke are the preferred solid starting materials, particularly coke and char.- coal ofV low ash content. coke breeze are particularly suitable. The process utilizes raw material which .in other processes suffer particular disadvantages.

The solid oxygen carriers employed .in place of air in accordance with this invention are particularly metal oxides which remain solid, Which will not sinter at the process temperatures andI which may be readily regenerated by oxidationl with air below the sintering temperature. The

oxide employed must possess ay sufficiently high. suitable metal oxides arey ferric oxide, cupric oxideon a clay or suitable;

oxidation potential.

carrier, vanadium pentoxide, stannic oxide, etc. It will be noted that all of these oxides have an oxidation potential sufcientlyhigh so that under equilibrium conditions (in temperature range involved) they will convert` carbon substantially quantitatively to COz. Ferric oxide, FeaOs, either pure or in the form of ores rich in FezOz,

is the preferred oxidilzing agent due to its avail-- ability and low cost. The metal oxide employedin the process may become contaminated with ash. and coke and eventually diluted down to a point where it must be discarded, hence the necessity for a cheap oxide. Furthermore, ferric oxide is extremely practical and presents no problems from an operationalstandpoint. A low grade iron ore can beemployed. at the expensel of circulating more raw material. However, such a procedure isv e'conomicalV when employed in a fluid system as will be described.` It is permissible to circulateabout 40 to 50.1bs. of solid oxide for every pound'of COztaken off as product. When FezOz is employed it is preferably not reduced substantially below the FeaOzr oxide.

It is suggested that atmost of the FezOs,

preferably 50-75.%/ be. reduced to FezOzz during the reaction between FezOaand the carbonaceous material.

The solid Oxygen Carriers of this invention may be employed in a finely-divided form and contacted with the carbonaceous raw materials either in the Vform of afluidized mass or a moving bed. The carbonaceous raw materials When solid are likewise preferably used in afinely-divided state.

perfect contact between the solids, ideal` temperature control andlgreatest. uniformity of'reactant' distribution throughout the fiui'di'ze'd` mass; Asa result'the process is extremely flex- Charcoal finesandv The fluidized state ofA the reactants affords.

ible and may be readily controlled at the desired degree of carbon oxidation. Since the only oxygen available in the reaction zone is bound in the form of a metallio oxide, the product remains free of inert gases, such as nitrogen.

In order to obtain proper fiuidization all solid reactants should be ground to a size that substantially all of it will pass through 100-mesh screen. For the best results, the ground solids should include a wide range of particle sizes, ranging upwardly from about 20 microns to about 100-mesh with a large proportion of the material between about 100 and ZOO-mesh.

Fluidizationl is accomplished in the carbon dioxide generator by means of carbon dioxide vapors produced in the reaction'zone or separately introduced thereto. Small amounts of the COz product may be recycled to a lower portion of the reacting solids to assure uniform fluidization over its entire height. Superficial linear flow velocities of the fluidized gases Within the fluidized bed may vary between about 0.3 and 4 ft. per second for proper fluidization -of most practical solid reactants in the particle sizes mentioned above.

' Spent solid Oxygen carrier is intermittently or continuously reoxidized with air in a separate reactor and returned tothe COz generation zone. In accordance with the preferred embodiment of the invention, the spent oxygen carrier consists principally of Fea04 and FezOz. This mixture may be conducted from the COz generation zone and contacted in the fiuidized state with air in a combustion zone to be reoxidized to FezOc, which is thereafter returned to the COz generation zone. Since the reoxidation reaction in the burner is highly exothermic, all or at least a substantial part of the heat required for the carbon oxidation by the iron oxide may be generated in the reoxidation stage and supplied to the carbon dioxide generator in the form of sensible heat of reoxidized iron oxide.

It has been found that carbonaceous materials will react with certain metallic oxides at a high rate at temperatures in the range of 500 C. to l200 C. For example, FezOa reacts with retort coke at temperatures between 1000 C. and 1200 C. Reaction between FezOz and wood charcoal sets in at about 750 C., while methane reacts with CuO supported on silica gel or Alundum at temperaturas as low as 600` C. In all instances the upper temperature limit to be employed is governed by the sintering temperature of the oxide. For this reason temperatures above 1200 C. are to be guarded against if not avoided altogether.

The reaction may be carried out in a twovessel or three-Vessel system employing fluidized solids, or the reaction may take place in a moving-bed or soaker-type reactor.

The reoxidation of the spent metallic o xide may be carried out, while avoidng sintering, at temperatures slightly higher than the reaction temperaturas, i. e., 1000 .-1200 C., preferably 1050 C. to 1l00 C.

In order to assure high reaction rates and to carry carbon oxidation in the COz generator as far as possible, it is preferable to employ a substantial stoichiometrical excess of FezOs over the oxidizable carbon present. Even if there should be unconverted carbon in the generator, the production of carbon monoxide therefrom will be negligible. Any carbon monoxide formed reacts rapidly with the FezOz to produce COz, but the carbon reacts only slowly with the COz thus produced at the temperature in the generator. In other words, the carbon will not react rapidly enough with the COz produced to form CO.

The nature of the present invention will appear more clearly from the following detailed description of the accompanying drawings in which each figure is a front elevation in diagrammatic form of one type of plant apparatus suitable for the practice thereof.

Figure 1 represents a two-Vessel system employing fiuidized solids. The system is preferably used when employing both solid and gasifiable carbonaceous material.

Figure 2 represents the moving-bed or soakertype reactor employed with solid carbonaceous materials. p

Figure 3 represents a system employing alternate moving beds of solid carbonaceous material and metallic oxide.

Referring to Figure 1 numeral I represents a carbon dioxide generator into which finely-divided carbonaceous material, such as coke, is led from hopper 2 via line 3. To aid in the flow of the carbonaceous material into Vessel l a small amount of an aerating gas, such as carbon dioxide, may be added through line 4. Numeral 5 represents a hopper containing finely-divided solid metallic oXide, for example iron oXide. The finely-divided iron oxide enters an upper portion of oxidation zone 'i via line 6. In initiating the process an initial charge of iron oxide may be mixed with carbon and the mixture heated in Vessel 1 'by means of combustion between the carbon and air entering through line 8 without reduction of the iron oxide. The hot iron oxide collects in withdrawal well 24 and is withdrawn from vessel l and passed under the pseudohydrostatic pressure in a fluidized condition via line 9 into generator I, preferably at an upper level. In generator l a temperature of 800 C. to 1000 C., preferably 900O C. to 950 C. is maintained, the heat required being supplied substantially by the sensible heat of the hot oxide. At this temperature reaction occurs between the solid carbonaceous material such as coke, supplied through line 3, and FezOs, forming COz. The Fe2-O3 introduced into Vessel l may be maintained in stoichiometrical excess over the oxidizable carbon present.

In operating, using nely-divided coke as the carbonaceous material and FezOz as the oxidizing agent, generator i contains above grid 35 a fluidized mass consisting substantially of FezOa introduced via line 9 at a point above the uppermost tray 43 and overfiowing through overflow weirs 4!! to the lower trays 43. The FezOz; has a particle size generally of to 200 mesh. The temperature of the FezOz in the generator is held at about 800 to l000 C. Finely-divided coke is supplied through drop, leg 3 at an hourly rate of about 0.01 to 0.05 lb. per lb. of FezO fed to the generator. The heat necessary to sustain the reaction: C--6FezO:-COz-i-zF'ezOit is supplied by the sensible heat of the FezOz introduced to the generator as will be later explained or additional heat may be added if required or desired by conventional means such as by coils 33 contained within the fluidized beds on one or more of the various trays 43.

The generator unit is best started up by introduction into the bottom thereof of hot combustion gases for both fluidization and heat supply. When the temperature is brought up sufficientlyso that active interaction of the coke and FezOz sets in, recycle of top gases to the bottom of the 5. generator for fluidization is started. This soon purges gasesv other than CO; from the unit. However,` external COz may, if desired, be introduced to expedite this purging and fluidization. In order that the carbon'contained in the coke be substantially completely converted to COz a countercurrent system is provided. For this purpose generator I contains trays 43 provided With overflow levels or down-comers 4d at intervals throughout the Vessel. The number of trays may be Varied according to the capacity of the Vessel and the extent of the oxidation required. The fluidized materials entering the generator through lines 3 and 9 build up on the tray until the level of the overflow is reached, after Which the fluidized materials pass downwardly in succession to the next lower level. The depth of the bed on each tray is preferably about 2 to 3 ft. The flow of fluidized materials occurs countercurrent to the upward fiow of fluidizing gas entering the Vessel through line 3!. I-lowever, the flow rate of the gas is controlled so as not to interfere with the overall downward flow of the fluidized solids.

Substantially pure COz amounting to about 0.2 to 0.9 mol per atom of carbon in the coke charged and containing suspended solids is withdrawn overhead from generator I, passed through cyclone I and recovered through line I I substantially free of entrained solids. The recovered gas is further worked up by condensation and/or absorption by conventional means not shown. Solids separated in cyclone It may be returned toV the fiuidized mass through pipe I2. Particles ofv undesirably small size or excess may be discarded through line I3.

Part of the COz produced is removed from line II via line I :l and introduced into the bottom of generator I, with the aid of blower 45 to ma intain uniform fluidized conditions throughout the sclids in the generator. Aerating lines I5 and IB equipped With Valves are provided to introduce aerating gas, such as COz into line 9, diluting the solid phase fiowing therethrough, th/usfacilitating its flow into Vessel I.

When the oxidation of the coke to (302 in vessei I has proceeded to the proper point, the spent solids contained in Vessel I are removed and passedunder the pseudo-hydrostatic pressure of the fluidized mass through withdrawal well and standpipe 'I'i with the assistance of dilution air entering throughline IB and carriedintoan upper portion of` regenerator 7 via line IB. Additional aeratinggas may besupplied through lines 32 and. 34; Standpipe Il may be enlarged in area soasto serve as a soaker in order to more completely'rernove vcarbon from the withdrawn solids. 'Ilhe solid materials thus removed contain reactedziron oxide in the form of Fe304, some uncOnVertedFezOs and carbon, and ash. -To maintam satisfactory oxidation rates in-generator I, theEezOs. content of the mixture is not allowed tofallflbelow by weight, preferably not below ZO-.to 50% by weight of the total iron oxides. The amount of carbon carried out through line Il into regenerator l depends upon the reactivity of the-.carbon toward the metallic oxide, which depends largely upon the character of the carbonaceous material. l-Iowever, the amount of carbonleavingv generator I can be low, for example, about 0.1V to about 1 weight percent of the .uidized oxiderecycled to the regenerator. 'Ijhe morezfcarbon putinto generator l, other operating conditions unchanged, the more 002 is produced; however, the more carbon must be aeee-71 6-. burned. in regenerator 1- Whae ma demandar pure COe isequivalent to only, a' limited fraction of the carbon in the fuel which must bezburflnt to get vheat required for other processes, as in a boiler plant, running high carbon 'contei'it` in generator I can bel very advanta'geous. Thus, even using a highly inert retort cokeV of lowv reactivity, by carrying about 3% of carbon in the,

oXide leaving generator I, one can produce over a third of a ton of pure COz per day per square foot of cross section in that unit With a net .bed depth in it of 40 ft., at atmospheric pressure and an operating temperature of 1000 C. Even With no counterflow in Vessel I, about 25% of the carbon in the fuel is obtained in` the form of pure COz from generator I, the restbeillg used for heat production in l.

larger productions of COz from it, reduce itsy height, recover far higher fractions of the total carbon of the fuel as pure COz from Vessel I, or combine these advantages as seems most desirable under any specific set of circumstances.`

I-ligh ash content carbonaceous material. causes rapid build up of ash in the ironV oXide to be recycled and this ash build upis not desirable. Air of substantially atmospheric pressure to fiuidize and oxidize the solids and Which 'may be preheated to a temperature as high as about 10700` to 1200 C. by heat exchange With the hot gases emerging from regenerator 'I Via line 20, is introduced into regenerator I'I Via lines IE and 2I,

entering at the lower portion of regenerator 'l= V through a perforated distribution plate-of grid 22. ln regenerator 'I any carbon carriedover from generator I is burned with excess air and the Fes04 becomes reoxidized to FezOs. A temperature of 1000 to 1200 C., preferably 1050 to 1100 C. is maintained in regenerator 7 and1 the reaction proceeds according to the equation;

4Fe3 O4+Oz 6Fez03 The superficial linear gas velocity within regenerator 'I is preferablyv maintained at about 0.5 to 3 ft. per second to establish an apparent bed density up to about 70 tolbs. per cubic ft. and a bed height between grid 22 and level 23 of about 5 to 15 ft.

The reoxidized iron oXide is Withdrawn under the pseudo-hydrostatic pressure of-the fluidized mass via withdrawal well and standpipe 24, and returned to generator I via line 9 entering near the top thereof. Aerating lines I 5, I 6 and 25 equipped with Valves are provided for introduction of fiuidizing and purge gas, suchas CO2, to dilute and strip the solid phase of the fiuidized mixture and to assist in its fiow to Vessel I Where the cycle is repeated. through lines I and I6 serves to purge the fluid of any remaining traces of nitrogen and air which may be contained therein, as it is desirable to keep all but traces of nitrogen from generator I'. Hot

The heat is. recovered in. coil 26, which functions best asthe Water tubes,

Carbon dioxide introducedv avacae'r 7 generator 'I via line 9 to generator I is, therefore. of a higher temperature than that of the solids in generator I, so that any net heat required in generator I may be supplied by circulating adequate amounts of solids from regenerator 'I to generator I. A solids circulation of about 80 to even as high as 400 lbs. between the vessels per lb. of carbonaceous material charged is generally sufiicient to satisfy the oxygen and heat requirements of the system. The amount of metal oxide transferred from regenerator 'I to generator I should be as small as possible and should not exceed that required for the desired heat supply to generator I. However, it is within the scope of this invention to add to the metal oxide entering generator I a small amount of other solid materials such as alkaline carbonates and oxides which may catalyze the reaction in generator I. Even inert heat carriers may be added. Of course, heat may be supplied to generator I through coil 33 or by other conventional means, if required. The temperature in regenerator 'I may be readily kept within the desired range by conventional cooling means, e. g., by cooling coils 26 which may be inserted in the Vessel or preferably by withdrawing a portion of the hot solids Via line 38, passing the hot solids with the assistance of dilution air from pipe III through an external cooler 39 operating as a Waste heat boiler and returning the cooled solids to the vessel 'I Via line 40. It is also within the scope of this invention that the Oxygen content of the solids circulated to the reaction zone may beso controlled that any desired proportion of these solids may act as inert heat carriers.

Withdrawal Wells and standpipes I'I and 24 in vessels I and 1 respectively are located as far as possible from the end of the standpipes supplying the charges to the respective vessels. vessels I and 'I are provided with cyclone separators II! and 21 for removal of finely-divided material from the outgoing gases, such as iron oxde or carbon nes, which are too small in size to remain iiuidized. The cyclone separators are equipped with dip legs I2 and 28 respectively for return of solids to the dense bed. Materials which are too small in size to remain fluidized are withdrawn via lines I3 and 29 respectively. This material will also contain some ash produced in the system. Any fly ash not retained by the separators4 can be removed from the gas streams leaving the vessels through lines I I and respectively by suitable means, such as scrubbing, if desired. From some fuels fiy ash forming in Vessel 1 tends to collect and float at a point near the top of the fluidized mass indicated by the level 23. Periodically a portion of this material is removed Via line 30 and discarded in order to prevent build-up.

The fiuidized solids in Vessel I are maintained at an apparent density of 70 to 80 lbs. per cubic ft. The Suspension in regenerator 1 may be of greater apparent density, averaging about 100 to 120 lbs. per cubic ft. The material fiowing through lines 9 and I9 into vessels I and 'I respectively are maintained at a lower apparent density of approximately 50 to 60 lbs. per cubic ft.

Once the process is in operation the only additional iron oxide required is make-up material required to supplant that which becomes too fine to fluidize or which is lost by dilution with ash.

Any manner of obtaining effective countercurrent flow between the fluidized oxide and carbon in the generator is desirable. For example, the

systempreyiously described may be employedor.

a moving bed type reactor may be used. Temperatures in the generator should be uniformly maintained between 800 and 1000 C. If lower temperatures are employed the reaction rate is too low resulting in low capacity. If higher temperatures are employed difficulties such as sintering or fusion are likely to be encountered.

The system described may be operated at atmospheric or superatmospheric pressure. It is preferred to operate the generator under superatmospherc pressure and the regenerator under atmospherc pressure.

The apparatus described in Figure l is also ideally suited for the conversion of gaseous and gasifiable hydrocarbons to 002. Such hydrocarbons, e. g., methane, may be introduced in Vessel I via line 35 controlled by Valve 31. The hydrocarbon gas passes upwardly through grid 35 and contacts the iron oxide. In this case counterflow of solids and gas in Vessel I is unnecessary and bed depth in generator I can be as low as a few feet. However, it is very desirable to maintain a considerable excess flow of FezOs through vessel I relative to the CI-Ii fed to assure the presence of FezOs throughout the bed and in the solids effluent from it. At the temperature of the iron oxide the hydrocarbon reacts with the iron oxide to produce COz and HzO which emerge from vessel I Via line I I. The water is removed from the COz by conventional means not shown. The hydrocarbon vapor entering the system Via line 36 may be pre-heated to a temperature short of cracking before introduction into Vessel I.

VSolids circulation between vessels I and 'I may also be accomplished by arranging the vessels at different levels and using `standpipes and dilute solids in gas suspensions to accomplish downward and upward now respectively in a manner known in the art of fluid solids handling.

It will be understood that the gases used for fluidizing the various solids transfer lines and for purgng purposes, should be selected so as not to interfere with the reactions intended, for example, air may be employed as a fiuidizing means supplied in lines I8, 32 and 34. I-Iowever, carbon dioxide or other suitable gas is used in lines I5, IG and 25. Air or nitrogen is not to be used as the fluidizing gas at the latter points since it is not desirable to contaminate the COz product with nitrogen.

While a two or more Vessel system of the type illustrated is essential for a continuous production of COz, it is noted that intermittent operation carried out in a single Vessel in a make and blow" manner is likewise within the scope of the present invention. In this case the make period Will be operated substantially at the conditions outlined above for generator I and the blow period at those conditions outlined for regenerator 'I as will be readily understood by those skilled in the art.

Figure 2 represents a diagrammatic sketch of apparatus employed in carrying out the process with the soaker-type or moving bed reactor. Referring to Figure 2, numeral I represents a reaction Vessel to the upper end of which are added carbonaceous solids via line 2 and hot metallic oxide, e. g., FezOs, via line 3. It is also possible to mix the two solids before introduction into Vessel I. The solids are allowed to fill the vessel and thereafter flow through the Vessel at a predetermined rate controlled by the operation of Valve 9. The solids undergo reaction during passageV downwardly in the Vessel I according to the equation C+6Fe203-C02+4Fe304. The C02-` generated passes ,up throughfthe solids and is removed vialine *5. In ve'ssel 'I.V the `Vsolids settle at a Vpre'de'ter'mined rate without Vturbulenc'e or with on1y a minimum amount of turbulence. To assure complete conversion of "icarbon .provision lis made for the introduction of small `'amounts of COz'g'as 'into 'the bottom of the reaction vessel from line l v'ia line land pump 8. The reduced metallic oxide is removed from Vessel I via line at a predetermined 'rate and is conveyed to a regenerator not shown by the assistance of aerating gas such as air introduced via line S. The regeneration operation and return of re-oxidized solids to line 3 is the same as'that described in connection with Figure 1.

Figure 3 represents the alternate bed type lof reactor. In Figure 3 alternate beds of metallic oxide contained in oXide chambers I are superimposed upon beds of carbonaceous solids such as charcoal contained in carbon Chambers 2, etc. In initiating the process each of .the oXide cham- -bers I is filled with hot oxide entering the uppermost chamber via line 5 and .passing via line 'I to the next lowermost chamber, etc. Similarly the solid carbonaceous material enters uppermost carbon chamber 2 via line 6 and proceeds to flow downwardly via 'line :8 -until *each of lthe carbon chambers contain 'the Idesired level of carbonaceous material. When the process has been initiated metallicoxide and carbonaceous solid arefed to the Vrespective cham'fb'er'sat a uniform rate 'determined 'by ythe rate of withdrawal 'of the solids from. 'the lowermost carbon and oxide chambers respectively. In starting up the process COz is produced in the lowermost oXide chamber, e. g., by passing a mixture of CO and COz Via line 3 into the lowermost metallic oXide chamber l. Or charcoal may be reacted with an excess of metallic oxide in the lowermost oXide chamber. The gases pass upwardly through the oxide bed during which passage the CO is converted substantially to COz. The COz stream is taken off the oxide chamber via line li and is introduced into the bottom of the lowermost carbon chamber 2. through the bed of carbonaceous material and 'is reduced to a mixture of CO and COz by the reaction: COz-i-CeZCO. This mixture of CO and COz is withdrawn via line I2 and is introduced into the bottom of the next lowermost metallic oxide chamber whereby the cycle is repeated. As many pairs of alternate beds may be employed as desired. The final COz product is withdrawn via line d overhea-d from the uppermost metallic oxide bed thus assuring the absence of CO in the final product. Spent metallic oXide is withdrawn from lowermost oXide chamber via line 9 and sent to a regenerator as described in connection with Figure 1. The hot regenerated metallic oxide is re-introduced into the reaction system via line 5. A continuous supply of carbonaceous material is furnished to the system via line 8. Any unreacted carbon from the lowermost carbon chamber is withdrawn via line E5 and returned via line Ill to supply line G. Ash build-up is prevented by periodic withdrawal of part of the carbon via line Ie. In the system described in Figure 3 mixing of the metallic oXide and solid carbon is entirely prevented.

The initial gaseous mixture of CO and COz fed to the reaction system is obtained by oxidizing carbonaceous material with metallic oxide. Once the reaction is under Way part of the CO and COz `mixture leaving one of the carbon chambers The COz passes upwardly E may be bled off and introduced into thai-lowermost metallic oxide chamber, e. g., via-line I4.

When CuO on a suitable carrier is 'employed in place of FezOs as the source of 'Oxygen infithe processes of Figures 1 and 2 heat is available 'in both the COz generator and in the regenera'tor due to the exotliermic character of both lreactions. In this event it Vis 'preferred to remove heat from only one of the vessels, e. g., 'bywithdrawing a stream of hotisolids fromthe tlreger'ierator, cooling the withdrawn stream 'in Ian external cooler and vreturning the 'cooled 'streamffto tlffe regenerator. This coolinglfeature is 'illustrated in Figure -1. l

This invention will be 'further illustrated by the following specific example. v

An operation that will give a high 'yield on the carbon employed is secured by 'usingf'as raw materiala wood'charcoal dust. For'theproduction of about tons per dayofCOz'iis'iiig FezOs having an average partcle size of V1100 to 400 mesh Ias the oxidizing agent in a system 'o'f the type illustrated by the drawing, the 'following approximate Vconditions have been foi'ffil suitable:

Generator temperature v1000-10500 .jC. Average generator .pressure Va lbs./sqiin. gauge. Regeneration temperature-- 1050-11-00 C. Charc'oal feed rate, lbs. per

The carbon dioxide produced under these conditions has a composition about as follows:

Percent 002 98 CO 1 Nitrogen 2 While the foregoing description and exemplary Operations have served to illustrate specific applications and results of the invention, other modifications obvious to those skilled in the art are within the scope of the invention. Only such limitations should be imposed on the invention as are indicated in the appended claims.

What is claimed is:

1. A process for preparing pure COa substantially free of non-condensible gases which comprises Contacting carbonaceous material in a reaction zone with solid finely-divided higher metal oxide selected from the group consisting of ferric oXide, vanadium pentoxide and stannic oXide, maintaining the solids content in the reaction zone in a fluidized state by means of infected 002 gas and at a temperature of 500 C. to 1200 C whereby the carbonaceous material is oxidized to CO: and the metal oXide reduced to a lower oXide, removing substantially pure 002 from an upper part of the reaction zone, removing from the reaction zone a stream of solid higher and lower metal oxides containing at least 10 weight per cent of the higher oxide, introducing the Withdrawn stream into a separate oxidation zone wherein the lower oxide is reoxidized to the higher oxide by means of a free oxygen-containing gas and the exothermic heat of reaction imparted to the oxide, withdrawing a stream of hot reoxidized higher metal oxide from the oxidation zone, purging the hot higher metal oxide of non- `condensible gases by means of COz gas injected -into the withdrawn stream, separating the purged non-condensible gases from the hot oxide, and returning hot purged higher metal oxide iiuidized CO'z and FezOs reduced to FezO. removing sub- .stantially pure COz from an upper part of the reaction zone, removing from the reaction zone a stream of solid FezOa and FezO. containing at least weight per cent of FezOs, introducing the .withdrawn stream into a separate oxidation zone wherein the FesO is reoxidized toFezOi` by means of air` and the exothermic heat of reaction imparted to the FezOz, withdrawing a stream of hot FezOz from the oxidation zone, purging the hot `ZE'ezOa of air and gaseous combustion products by means of COz gas injected into the Withdrawn stream separating the purged gases from the hot FezOz and returning the hot FezOa fluidized in COz' to the reduction zone.

3. A process according to claim 2 in which the carbonaceous material is natural gas.

12 4. A process according to claim 2 in which the carbonaceous material is methane.

5. AV process according to claim 2 in Which the carbonaceous material is finely-divided coke.

6. A process according to claim 2 wherein the FezO: content of the oxides in the reaction zone is maintained between 25 and Weight per cent.

WARREN K. LEWIS. EDWIN R. GILLILAND.

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McPherson and Henderson's General Chemistry, 3rd ed., pp. 590-593, Ginn and Co., N. Y.

Thorpe's Dictionary of Applied Chemistry, vol. 7, 4th ed., pages 32, 33. Longmans, Green and Co., N. Y. 

1. A PROCESS FOR PREPARING PURE CO2 SUBSTANTIALLY FREE OF NON-CONDENSIBLE GASES WHICH COMPRISES CONTACTING CARBONACEOUS MATERIAL IN A REACTION ZONE WITH SOLID FINELY-DIVIDED HIGHER METAL OXIDE SELECTED FROM THE GROUP CONISTING OF FERRIC OXIDE, VANADIUM PENTOXIDE AND STANNIC OXIDE, MAINTAINING THE SOLIDS CONTENT IN THE REACTION ZONE IN A FLUIDIZED STATE BY MEANS OF INJECTED CO2 GAS AND AT A TEMPERATURE OF 500* C. TO 1200* C. WHEREBY THE CARBONACEOUS MATERIAL IS OXIDIZED TO CO2 AND THE METAL OXIDE REDUCED TO A LOWER OXIDE, REMOVING SUBSTANTIALLY PURE CO2 FROM AN UPPER PART OF THE REACTION ZONE, REMOVING FROM THE REACTION ZONE A STREAM OF SOLID HIGHER AND LOWER METAL OXIDES CONTAINING AT LEAST 10 WEIGHT PER CENT OF THE HIGHER OXIDE, INTRODUCING THE WITHDRAWN STREAM INTO A SEPARATE OXIDATION ZONE WHEREIN THE LOWER OXIDE IS REOXIDIZED TO THE HIGHER OXIDE BY MEANS OF A FREE-OXYGEN-CONTAINING GAS AND THE EXOTHERMIC HEAT OF REACTION IMPARTED TO THE OXIDE, WITHDRAWING A STREAM OF HOT REOXIDIZED HIGHER METAL OXIDE FROM THE OXIDATION ZONE, PURGING THE HOT HIGHER METAL OXIDE OF NONCONDENSIBLE GASES BY MEANS OF CO2 GAS INJECTED INTO THE WITHDRAWN STREAM, SEPARATING THE PURGED NON-CONDENSIBLE GASES FROM THE HOT OXIDE, AND RETURNING HOT PURGED HIGHER METAL OXIDE FLUIDIZED IN CO2 TO THE REACTION ZONE. 